U.S. patent application number 13/216442 was filed with the patent office on 2012-03-01 for multimode frontend circuit.
This patent application is currently assigned to NTT DOCOMO, INC.. Invention is credited to Kunihiro Kawai, Shoichi Narahashi, Hiroshi Okazaki.
Application Number | 20120049985 13/216442 |
Document ID | / |
Family ID | 44785241 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120049985 |
Kind Code |
A1 |
Kawai; Kunihiro ; et
al. |
March 1, 2012 |
MULTIMODE FRONTEND CIRCUIT
Abstract
A multimode frontend circuit of the present invention comprises
two transmission paths. Each of the transmission paths comprises
two input/output lines, a first transmission line having one end
connected to one of the input/output lines and the other end
connected to the other input/output line, a second transmission
line connected to the one of the input/output lines and the other
end connected to the other input/output line, and one or more
termination switch circuits. The termination switch circuit or
circuits comprise a switch having one end connected to one of the
first and second transmission lines and a termination circuit
connected to the other end of the switch. Each of the transmission
lines may comprise one or more short-circuiting switches. The
short-circuiting switch or switches are capable of short-circuiting
between the two transmission lines at positions at the same
electrical length from one of the input/output lines.
Inventors: |
Kawai; Kunihiro;
(Yokohama-shi, JP) ; Okazaki; Hiroshi; (Zushi-shi,
JP) ; Narahashi; Shoichi; (Yokohama-shi, JP) |
Assignee: |
NTT DOCOMO, INC.
Chiyoda-ku
JP
|
Family ID: |
44785241 |
Appl. No.: |
13/216442 |
Filed: |
August 24, 2011 |
Current U.S.
Class: |
333/22R |
Current CPC
Class: |
H01P 1/203 20130101;
H01P 1/2135 20130101; H03H 7/465 20130101 |
Class at
Publication: |
333/22.R |
International
Class: |
H01P 1/24 20060101
H01P001/24 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2010 |
JP |
2010-188393 |
May 23, 2011 |
JP |
2011-114894 |
Claims
1. A multimode frontend circuit comprising first, second and third
ports, a first transmission path between the first and second
ports, and a second transmission path between the first and third
ports, each of the transmission paths comprising: two input/output
lines; a first transmission line having one end connected to one of
the input/output lines and the other end connected to the other
input/output line; a second transmission line having one end
connected to the one of the input/output lines and the other end
connected to the other input/output line; and one or a plurality of
termination switch circuits; wherein: the electrical length of the
first transmission line is equal to the electrical length of the
second transmission line; a characteristic impedance for an even
mode and a characteristic impedance for an odd mode of the first
transmission line are constant along the length of the first
transmission line; a characteristic impedance for an even mode and
a characteristic impedance for an odd mode of the second
transmission line are constant along the length of the second
transmission line; the characteristic impedance for the even mode
of the first transmission line is equal to the characteristic
impedance for the even mode of the second transmission line; the
characteristic impedance for the odd mode of the first transmission
line is equal to the characteristic impedance for the odd mode of
the second transmission line; and each of the one or plurality of
termination switch circuits comprises a switch and a termination
circuit, one end of the switch being connected to one of the first
and second transmission lines, the termination circuit being
connected to the other end of the switch.
2. The multimode frontend circuit according to claim 1, wherein the
first and second transmission lines have the same length and the
same line width and the distance between the first and second
transmission lines is constant along the length of the first and
second transmission lines.
3. The multimode frontend circuit according to claim 1, wherein:
included among the termination switch circuits of the transmission
paths is a set of termination switch circuits connected to the
different transmission lines at points at the same electrical
length from one of the input/output lines.
4. The multimode frontend circuit according to claim 1, wherein:
each of the transmission paths comprises one or more
short-circuiting switches; and the one or more short-circuiting
switches are capable of short-circuiting between the first and
second transmission lines at points at the same electrical length
from one of the input/output lines.
5. The multimode frontend circuit according to claim 4, wherein:
included among the termination switch circuits and the
short-circuiting switches is a termination switch circuit and a
short-circuiting switch that are connected at the same position on
the first or second transmission line.
6. The multimode frontend circuit according to claim 4, wherein:
the number of the short-circuiting switches is greater than or
equal to two; and included among the termination switch circuits is
a termination switch circuit connected to the transmission line
between positions at which two of the short-circuiting switches are
connected.
7. The multimode frontend circuit according to claim 1, wherein the
termination circuit is a reactance circuit.
8. The multimode frontend circuit according to claim 7, wherein the
reactance circuit is a variable reactance circuit.
9. The multimode frontend circuit according to claim 4, further
comprising a function selector switch for alternately connecting
and disconnecting the second and third ports to each other, wherein
each of the transmission paths comprises two or more of the
termination switch circuits and four or more of the
short-circuiting switches.
Description
TECHNICAL FIELD
[0001] The present invention relates to a multimode frontend
circuit performing transmission and reception.
BACKGROUND ART
[0002] In the field of wireless communications using radio waves, a
technique called Frequency Division Duplex (FDD) in which one
frequency band is used to transmit and another is used to receive a
transmission is used in communication schemes such as W-CDMA. If a
station uses one antenna to perform the bidirectional
communication, the station uses a duplexer to prevent a signal
transmitted from the station from entering a system that directly
receives signals from other stations. The frequency characteristics
of the duplexer is typically invariant. Therefore, for example in a
communication device that uses multiple frequencies or bandwidths,
duplexers for the respective frequencies or bandwidths are provided
and a switch is used to make switching between them (Masaaki Koiwa,
Fumiyoshi Inoue, and Takashi Okada, "Multiband Mobile Terminals",
NTT DoCoMo Technical Journal Vol. 14, No. 2, pp. 31-37, July,
2006).
[0003] There is another technique called Time Division Duplex (TDD)
in which transmission and reception are performed with the same
frequency in different timings. In the TDD, sharing of an antenna
is generally accomplished by using a switch. Global System for
Mobile Communications (GSM), which is not a TDD system, makes
switching between transmission and reception using a switch, like
the TDD. Accordingly, terminals supporting the GSM use a switch to
use an antenna for both transmission and reception. Mobile
terminals that support both W-CDMA, which uses FDD, and GSM include
transmission/reception systems for both schemes and use a switch to
make switching between the systems (Takashi Okada, "Mobile Terminal
RF Circuit Technology for Increasing Capacity/Coverage and
International Roaming", NTT DoCoMo Technical Journal Vol. 16, No.
2, pp. 45-53, July, 2008). Since TDD uses the same frequency for
transmission and reception, the duplexer described above cannot be
provided in transmission and reception paths. Therefore, a
communication device that supports both FDD and TDD requires
transmission/reception systems for FDD and transmission/reception
systems for TDD.
[0004] However, these methods have a problem that the circuit area
and the number of components increase as the number of frequencies
or bandwidths used increases. Furthermore, the need for
transmission and reception circuits for both FDD and TDD also leads
to increase in the circuit area and the number of components.
[0005] In view of these circumstances, an object of the present
invention is to provide a circuit that function as both of a
duplexer whose frequency band and/or center frequency can be
changed and a switch for TDD, that is, to provide a multimode
frontend circuit.
SUMMARY OF THE INVENTION
[0006] A multimode frontend circuit of the present invention
comprises first, second and third ports, a first transmission path
between the first port and the second port and a second
transmission path between the first port and the third port. Each
of the transmission path comprises two input/output lines, a first
transmission line having one end connected to one of the
input/output lines and the other end connected to the other
input/output line, a second transmission line having one end
connected to the one of the input/output lines and the other end
connected to the other of the input/output lines, and one or more
termination switch circuits. The electrical length of the first
transmission line is equal to the electrical length of the second
transmission line. The characteristic impedance for the even mode
and the characteristic impedance for the odd mode of the first
transmission line are constant along the length of the first
transmission line. The characteristic impedance for the even mode
and the characteristic impedance for the odd mode of the second
transmission line are constant along the length of the second
transmission line. The characteristic impedance for the even mode
of the first transmission line is equal to the characteristic
impedance for the even mode of the second transmission line. The
characteristic impedance for the odd mode of the first transmission
line is equal to the characteristic impedance for the odd mode of
the second transmission line. The termination switch circuit
comprises a switch having one end connected to one of the first and
second transmission lines and a termination circuit connected to
the other end of the switch. Each of the transmission paths may
comprise one or more short-circuiting switches. The
short-circuiting switch or switches are capable of short-circuiting
between the two transmission paths at points at the same electrical
length each other from one of the input/output lines.
EFFECTS OF THE INVENTION
[0007] The multimode frontend circuit of the present invention
enables setting of a transmission frequency and a rejection
frequency for each transmission path by turning on and off the
termination switch circuit and also enables switching between
transmission paths to transmit a signal according to time. That is,
the function of a duplexer whose bandwidth or a center frequency
can be changed and the functions of a switch for TDD can be
provided by the same circuit, that is, a multimode frontend
circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1A is a diagram illustrating a functional configuration
of a variable resonator described in an unpublished patent
application;
[0009] FIG. 1B is a cross-sectional view illustrating the
functional configuration of the variable resonator in the
unpublished patent application;
[0010] FIG. 2A is a diagram illustrating an exemplary configuration
of a switch circuit having a switch 150a one end of which is
directly grounded;
[0011] FIG. 2B is a diagram illustrating an exemplary configuration
of a switch circuit including a capacitor one end of which is
connected to a switch 150a and the other end of which is
grounded;
[0012] FIG. 2C is a diagram illustrating an exemplary configuration
of a switch circuit including an inductor one end of which is
connected to a switch 150a and the other end of which is
grounded;
[0013] FIG. 2D is a diagram illustrating an exemplary configuration
of a switch circuit including a transmission line one end of which
is connected to a switch 150a and the other end of which is
grounded;
[0014] FIG. 2E is a diagram illustrating an exemplary configuration
of a switch circuit including a transmission line one end of which
is connected to a switch 150a and the other end of which is
open;
[0015] FIG. 2F is a diagram illustrating an exemplary configuration
of a switch circuit including a variable capacitor with variable
capacitance one end of which is connected to a switch 150a and the
other end of which is grounded;
[0016] FIG. 2G is a diagram illustrating an exemplary configuration
of a switch circuit including a variable inductor with variable
inductance one end of which is connected to a switch 150a and the
other end of which is grounded;
[0017] FIG. 2H is a diagram illustrating an exemplary configuration
of a switch circuit including a transmission line one end of which
is connected to a switch 150a and the other end of which is
grounded;
[0018] FIG. 2I is a diagram illustrating an exemplary configuration
of a switch circuit including transmission lines connected in
series with each other through a switch and a switch 150a connected
to one end of one of the transmission lines;
[0019] FIG. 3A is a diagram illustrating an exemplary configuration
of a parallel resonator circuit whose first resonance frequency is
variable;
[0020] FIG. 3B is a diagram illustrating an exemplary configuration
of a parallel resonator circuit whose second resonance frequency is
variable;
[0021] FIG. 4 is a diagram illustrating a configuration of a
multimode frontend circuit of the present invention;
[0022] FIG. 5 illustrates a circuit model of the multimode frontend
circuit of the present invention functioning as a switch;
[0023] FIG. 6A is a diagram illustrating impedance Z.sub.ins1
between 4 and 6 GHz when L.sub.S1 is set at 10.degree.;
[0024] FIG. 6B is a diagram illustrating impedance Z.sub.ins1
between 4 and 6 GHz when L.sub.S1 is 80.degree.;
[0025] FIG. 7 is a diagram illustrating an S-parameter when
L.sub.S1 is set at 10.degree.;
[0026] FIG. 8 is a diagram illustrating an S-parameter when
L.sub.S1 is set at 80.degree.;
[0027] FIG. 9 is a diagram illustrating an another configuration of
the multimode frontend circuit of the present invention;
[0028] FIG. 10 illustrates a circuit model of another multimode
frontend circuit of the present invention functioning as a
switch;
[0029] FIG. 11A is a diagram illustrating impedance Z.sub.ins1
between 4 and 6 GHz when L.sub.S1 is set at 10.degree.;
[0030] FIG. 11B is a diagram illustrating impedance Z.sub.ins1
between 4 and 6 GHz when L.sub.S1 is set at 80.degree.;
[0031] FIG. 12 is a diagram illustrating an S-parameter when
L.sub.S1 is set at 10.degree.;
[0032] FIG. 13 is a diagram illustrating an S-parameter when
L.sub.S1 is set at 80.degree.;
[0033] FIG. 14 is a diagram illustrating a multimode frontend
circuit of the present invention functioning as a filter;
[0034] FIG. 15 illustrates a circuit model of the multimode
frontend circuit of the present invention functioning as a
filter;
[0035] FIG. 16 is a diagram illustrating frequency characteristics
of the multimode frontend circuit of the present invention
functioning as a filter when L.sub.SF1=80.degree.,
L.sub.FF2=180.degree. and L.sub.SF2 is changed between 10.degree.
and 20.degree.;
[0036] FIG. 17 is a diagram illustrating frequency characteristics
of the multimode frontend circuit of the present invention
functioning as a filter when L.sub.SF1=is 90.degree.,
L.sub.FF2=200.degree. and L.sub.SF2 is changed between 10.degree.
and 20.degree.;
[0037] FIG. 18 is a diagram illustrating an exemplary states of
switches of the multimode frontend circuit of the present invention
when used as a duplexer;
[0038] FIG. 19 illustrates a circuit mode of the multimode frontend
circuit of the present invention functioning as a duplexer;
[0039] FIG. 20 is a diagram illustrating frequency characteristics
of the multimode frontend circuit of the present invention
functioning as a duplexer when L.sub.DR1=180.degree.,
L.sub.D1.sub.--.sub.1=55.degree., L.sub.D1.sub.--.sub.2=17.degree.,
L.sub.DR2=164.degree., L.sub.D2.sub.--.sub.1=52.degree. and
L.sub.D2.sub.--.sub.2=17.degree.;
[0040] FIG. 21 is a diagram illustrating frequency characteristics
of the multimode frontend circuit of the present invention
functioning as a duplexer when L.sub.DR1=200.degree.,
L.sub.D1.sub.--.sub.1=65.degree., L.sub.D1.sub.--.sub.2=17.degree.,
L.sub.DR2=183.degree., L.sub.D2.sub.--.sub.1=62.degree. and
L.sub.D2.sub.--.sub.2=17.degree.;
[0041] FIG. 22A is a diagram illustrating an example of a
termination circuit directly grounded;
[0042] FIG. 22B is a diagram illustrating an example of a
termination circuit grounded through an inductor;
[0043] FIG. 22C is a diagram illustrating an example of a
termination circuit grounded through an inductor and a capacitor
connected in series;
[0044] FIG. 22D is a diagram illustrating an example of a
termination circuit using an open transmission line;
[0045] FIG. 22E is a diagram illustrating an example of a
termination circuit grounded through a capacitor;
[0046] FIG. 22F is a diagram illustrating an example of a
termination circuit grounded through an inductor and a capacitor
connected in parallel;
[0047] FIG. 22G is a diagram illustrating a termination circuit
grounded through a transmission line;
[0048] FIG. 22H is a diagram illustrating an example of a
termination circuit grounded through a variable inductor;
[0049] FIG. 22I is a diagram illustrating an example of a
termination circuit grounded through an inductor and a variable
capacitor connected in series;
[0050] FIG. 22J is a diagram illustrating an example of a
termination circuit grounded through a variable capacitor;
[0051] FIG. 22K is a diagram illustrating an example of a
termination circuit grounded through an inductor and a variable
capacitor connected in parallel;
[0052] FIG. 22L is a diagram illustrating an example of a
termination circuit grounded through a variable inductor and a
capacitor connected in series;
[0053] FIG. 22M is a diagram illustrating an example of a
termination circuit grounded through a variable inductor and a
capacitor connected in parallel;
[0054] FIG. 22N is a diagram illustrating an example of a
termination circuit grounded through a transmission line that can
be changed in length through a switch provided on the transmission
line;
[0055] FIG. 22O is a diagram illustrating an example of a
termination circuit grounded through a transmission line and a
variable capacitor connected in series;
[0056] FIG. 22P is a diagram illustrating an example of a
termination circuit in which two transmission lines are connected
in series through a switch;
[0057] FIG. 22Q is a diagram illustrating an example of a
termination circuit in which three transmission lines are connected
in series through switches;
[0058] FIG. 23 is a diagram illustrating a configuration of a
multimode frontend circuit of the present invention using a
variable LC resonator as a termination circuit;
[0059] FIG. 24 is a diagram illustrating frequency characteristics
of the multimode frontend circuit in FIG. 23 functioning as a
duplexer when L.sub.DR1=180.degree.,
L.sub.D1.sub.--.sub.1=48.degree., L.sub.D1.sub.--.sub.2=35.degree.,
L.sub.DR2=164.degree., L.sub.D2.sub.--.sub.1=65.degree.,
L.sub.D2.sub.--.sub.2=25.degree., C.sub.P1=0.2 pF, L.sub.P1=0.4 nH,
C.sub.P2=4.6 pF, and L.sub.P2=0.3 nH;
[0060] FIG. 25 is a diagram illustrating a configuration of a
multimode frontend circuit of a second embodiment;
[0061] FIG. 26 is a diagram illustrating a configuration of a
multimode frontend circuit 2000 functioning as a variable dual-band
filter;
[0062] FIG. 27 is a diagram illustrating the transmission
coefficient from a port 1001 to a port 2104 when electrical lengths
at 5 GHz are set as L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree., L.sub.TLout.sub.--1=20.degree.,
L.sub.in.sub.--.sub.1=57.degree., L.sub.1.sub.--.sub.1=180.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.3.sub.--.sub.1=10.degree., L.sub.4.sub.--.sub.1=155.degree.,
L.sub.5.sub.--.sub.1=155.degree., L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=73.degree., L.sub.1.sub.--.sub.2=160.degree.,
L.sub.2.sub.--.sub.210.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=155.degree., and
L.sub.5.sub.--.sub.2=11.degree.;
[0063] FIG. 28A is a diagram illustrating impedance in the example
in FIG. 27 at 5.62 GHz;
[0064] FIG. 28B is a diagram illustrating impedance in the example
in FIG. 27 at 5 Hz;
[0065] FIG. 29 is a diagram illustrating the transmission
coefficient from the port 1001 to the port 2104 when electrical
lengths at 5 GHz are set as L.sub.A.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=57.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=155.degree., L.sub.5.sub.--.sub.1=155.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=73.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=155.degree. and
L.sub.5.sub.--.sub.2=11.degree.;
[0066] FIG. 30A is a diagram illustrating impedance in the example
in FIG. 29 at 6.18 GHz;
[0067] FIG. 30B is a diagram illustrating impedance in the example
in FIG. 29 at 6 GHz;
[0068] FIG. 31 is the transmission coefficient from the port 1001
to the port 2104 when electrical lengths at 5 GHz are set as
L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=.degree., L.sub.in.sub.--.sub.2=0.degree.,
L.sub.1.sub.--.sub.2=145.degree., L.sub.2.sub.--.sub.2=10.degree.,
L.sub.3.sub.--.sub.2=10.degree.,L.sub.4.sub.--.sub.2=180.degree.
and L.sub.5.sub.--.sub.2=139.degree.;
[0069] FIG. 32A is a diagram illustrating impedance in the example
in FIG. 31 at 6.18 GHz;
[0070] FIG. 32B is a diagram illustrating impedance in the example
in FIG. 31 at 6 GHz;
[0071] FIG. 33 is a diagram illustrating the transmission
coefficient from the port 1001 to the port 2104 when electrical
lengths at 5 GHz are set as L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=8.degree., L.sub.3.sub.--.sub.1=8.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=0.degree., L.sub.1.sub.--.sub.2145.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=180.degree., and
L.sub.5.sub.--.sub.2=139.degree.; and
[0072] FIG. 34 is a diagram illustrating the transmission
coefficient from the port 1001 to the port 2104 when electrical
lengths at 5 GHz are set as L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=0.degree.,
L.sub.in.sub.--.sub.2=0.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=8.degree., L.sub.3.sub.--.sub.2=8.degree.,
L.sub.4.sub.--.sub.2=180.degree. and
L.sub.5.sub.--.sub.2=139.degree..
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0073] Before describing the present invention, part of Japanese
Patent Application No. 2010-049126 (filed on Mar. 5, 2010), which
is an unpublished patent application filed by the present
applicant, will be described first. Applications equivalent to the
basic Japanese patent application were filed in the U.S., Europe,
China and Korea with patent application numbers U.S. Ser. No.
13/040,717 (filed on Mar. 4, 2011), EP 11 156 817.6 (filed on Mar.
3, 2011), CN201110053567.1 (filed on Mar. 7, 2011) and
KR10-2011-0018451 (filed on Mar. 2, 2011).
[0074] FIG. 1A illustrates a variable resonator 100 having a
micro-strip line structure, which is one embodiment in Japanese
Patent Application No. 2010-049126. FIG. 1B is a cross-sectional
view of the variable resonator 100. The variable resonator 100
comprises two transmission lines 101 and 102 and multiple switch
circuits 150. In the embodiment illustrated in FIG. 1A, the two
rectangular transmission lines 101 and 102 are formed on a
dielectric substrate 805. One end 101a of the first transmission
line 101 is connected to an input line 111 formed on the dielectric
substrate 805 and the other end 101b of the first transmission line
101 is connected to an output line 112 formed on the dielectric
substrate 805. One end 102a of the second transmission line 102 is
connected to the input line 111 and the other end 102b of the
second transmission line 102 is connected to the output line 112.
The two transmission lines 101 and 102 are made of a conductive
material such as metal and are formed on one surface of the
dielectric substrate 805. A ground conductor 800 of a conductive
material such as metal is formed on the other surface (backside) of
the dielectric substrate 805. The dielectric substrate 805 is
exposed in the area, indicated by reference numeral 130, enclosed
by the two transmission lines 101 and 102, the input line 111 and
the output line 112.
[0075] Requirements of the two transmission lines 101 and 102 are
that:
[0076] (1) the electrical length of the first transmission line 101
is equal to the electrical length of the second transmission line
102;
[0077] (2) the characteristic impedance for the even mode and the
characteristic impedance for the odd mode of the first transmission
line 101 are constant along the length of the first transmission
line 101;
[0078] (3) the characteristic impedance for the even mode and the
characteristic impedance for the odd mode of the second
transmission line 102 are constant along the second transmission
line 102;
[0079] (4) the characteristic impedance for the even mode of the
first transmission line 101 is equal to the characteristic
impedance for the even mode of the second transmission line 102;
and
[0080] (5) the characteristic impedance for the odd mode of the
first transmission line 101 is equal to the characteristic
impedance for the odd mode of the second transmission line 102.
[0081] For example, if the dielectric substrate 805 has a uniform
thickness and a uniform relative permittivity over its length and
breadth, the two transmission lines 101 and 102 will satisfy
requirements (1) to (5) if the transmission lines 101 and 102 are
formed in such a manner that:
[0082] (a) the length of the first transmission line 101 is equal
to the length of the second transmission line 102;
[0083] (b) the line width of the first transmission line 101 is
equal to the line width of the second transmission line 102;
and
[0084] (c) the distance (indicated by D in FIG. 1A) between the
first transmission line 101 and the second transmission line 102 is
constant. In the variable resonator 100 illustrated in FIG. 1A, the
two transmission lines 101 and 102 have the same line length L and
the same line width W and are formed on the dielectric substrate
805 in parallel to each other at a distance D from each other with
a gap 130 between them, on the assumption that the dielectric
substrate 805 has a uniform thickness and a uniform relative
permittivity over its length and breadth.
[0085] If the dielectric substrate 805 does not have a uniform
thickness and/or relative permittivity, the two transmission lines
101 and 102 are formed so that requirements (1) to (5) are
satisfied by taking into consideration the thickness and
distribution of the relative permittivity of the dielectric
substrate 805. Such a design can be accomplished by any known
technique and therefore detailed description of the design will be
omitted.
[0086] The variable resonator 100 illustrated in FIG. 1A comprises
five switch circuits 150 (only one of the switch circuits is given
the reference numeral for simplicity of the drawing). In the
variable resonator 100, the switch circuits 150 are connected only
to the second transmission line 102. However, the present
embodiment is not limited to this configuration; the switch
circuits 150 need only to be connected to one of the first
transmission line 101 and the second transmission line 102. While
specific exemplary configurations of the switch circuits 150 will
be described later, each of the switch circuits 150 in the example
illustrated in FIG. 1A comprises a switch 150a one end of which is
connected to one of the first transmission line 101 and the second
transmission line 102 and the other end of which is grounded. Each
of the switches 150a has one end 831 connected to the second
transmission line 102 and the other end 832 electrically connected
to the ground conductor 800 through a conductor 833 and a via hole
806 as illustrated in FIG. 1B. There is no limitation on the shape
of the conductor 833 and therefore the conductor 833 is omitted
from the other drawings.
[0087] The switch circuits 150 are connected at [1] locations on
the first transmission line 101 at different electrical lengths
from one end 101a of the first transmission line 101 (locations
excluding the end 101a and the other end 101b) and at [2] locations
on the second transmission line 102 at different electrical lengths
from one end 102a of the second transmission line 102 (locations
excluding the end 102a and the other end 102b). In such a
configuration, the electrical length .theta..sub.1 from the
location on the first transmission line 101 at which a switch
circuit is connected to the end 101a is possibly equal to the
electrical length .theta..sub.2 from the location on the second
transmission line 102 at which a switch circuit is connected to the
end 102a. If .theta..sub.1=.theta..sub.2, the switch circuit
connected at the location on the first transmission line 101 at an
electrical length .theta..sub.1 from the end 101a and the switch
circuit connected at the location on the second transmission line
102 at a electrical length .theta..sub.2 from the end 102a should
not be turned on at the same time. When the variable resonator 100
is caused to operate as a resonator as described later, only one of
the switch circuits 150 is turned on. From this perspective, it is
useless to connect switch circuits 150 at the locations on the
first transmission line 101 and the second transmission line 102 at
an equal electrical length from the input line 111. Therefore, in
addition to requirements [1] and [2] described above, the following
requirement concerning the connection locations of the switch
circuits 150 may be set: [3] the electrical length of each switch
circuit 150 connected to one of the two transmission lines 101 and
102 from one end of the transmission line is not equal to the
electrical lengths of any of the switch circuits 150 connected to
the other transmission line from one end of that transmission
line.
[0088] In the variable resonator 100, when one of the switch
circuits 150 is turned on, a bandwidth corresponding to the
location at which the switch circuit is connected is provided; when
another switch circuit is turned on, another bandwidth
corresponding to the location at which that switch circuit is
connected is provided. Therefore, the bandwidth of the variable
resonator 100 can be changed by turning on a different switch
circuit.
[0089] FIGS. 2A to 2I illustrate exemplary configurations of the
switch circuits 150. A switch circuit 150 illustrated in FIG. 2A
has a switch 150a the other end of which is directly grounded. A
switch circuit 150 illustrated in FIG. 2B includes a capacitor one
end of which is connected to a switch 150a and the other end of
which is grounded. A switch circuit 150 illustrated in FIG. 2C
includes an inductor one end of which is connected to a switch 150a
and the other end of which is grounded. A switch circuit 150
illustrated in FIG. 2D includes a transmission line one end of
which is connected to a switch 150a and the other end of which is
grounded. In this configuration, the transmission line has a line
length equal to one quarter (1/4) wavelength at the operating
frequency in the on-state of the switch circuit. A switch circuit
150 illustrated in FIG. 2E includes a transmission line one end of
which is connected to a switch 150a and the other end of which is
open. In this configuration, the transmission line has a line
length equal to a half (1/2) wavelength at the operating frequency
in the on-state of the switch circuit. A switch circuit 150
illustrated in FIG. 2F includes a variable capacitance with
variable capacitance one end of which is connected to a switch 150a
and the other end of which is grounded. A switch circuit 150
illustrated in FIG. 2G includes a variable inductor with variable
inductance one end of which is connected to a switch 150a and the
other end of which is grounded. A switch circuit 150 illustrated in
FIG. 2H includes a transmission line one end of which is connected
to a switch 150a and the other end of which is grounded. One or
more switches are connected onto the transmission line and the
other end of each of the switches is grounded. By turning on and
off the switches, the characteristics of the switch circuit 150 can
be changed. A switch circuit 150 illustrated in FIG. 2I includes
transmission lines connected in series with each other through a
switch and a switch 150a connected to one end of one of the
transmission lines. By turning on and off the switch between the
transmission lines, the characteristics of the switch circuit 150
can be changed.
[0090] The switches 150a are not limited to contact switches. For
example, the switches 150a may be so-called switching elements,
such as diodes or transistors, for example, that have the function
of connecting and disconnecting a circuit without using a contact
on a circuit network. Alternatively, the switches 150a may be
switches using MEMS (Micro ElectroMechanical Systems) technology.
The switching elements are not limited to ohmic switches, which
pass direct current when the switching elements are on. The
switching elements may be capacitive switches, which block a direct
current but pass an alternating current when the switching elements
are on. Alternatively, as illustrated in FIGS. 3A and 3B, a
parallel resonant circuit whose resonance frequency can be changed
may be used. In this case, the characteristics of the parallel
resonant circuit are set so that the resonance frequency of the
parallel resonant circuit will be equal to the resonance frequency
of a variable resonator made up of two transmission lines 101 and
102 when the switch circuit 150 is to be turned off, and that the
resonance frequency of the parallel resonant circuit does not
resonate at the resonance frequency of the variable resonator made
up of the two transmission lines 101 and 102 when the switch
circuit 150 is to be turned on. For example, the resonance
frequency of the parallel resonant circuit can be changed by
changing the capacitance of a variable capacitor or the inductance
of a variable inductor, as illustrated in FIGS. 3A and 3B. The
configuration of the switch circuit 150 is not limited to those
described above. While the frequency characteristics of the
variable resonator can be changed as desired by varying the
configuration of the switch circuit 150, the resonance frequency of
the variable resonator is determined by the line length of the two
transmission lines 101 and 102 and therefore remains the same.
[0091] The foregoing is description of part of Japanese Patent
Application No. 2010-049126 that is at least required to explain
the present invention. However, the present invention is not
limited to the specifics described above. Other specifics in
Japanese Patent Application No. 2010-049126 can also be applied to
the present invention. Embodiments of the present invention will be
described below in detail. Components having like functions are
given like reference numerals and repeated description thereof will
be omitted.
First Embodiment
[0092] FIG. 4 illustrates a configuration of a multimode frontend
circuit of a first embodiment. The multimode frontend circuit of
the first embodiment may be fabricated with micro-strip lines. The
multimode frontend circuit 1000 comprises three ports 1001, 1002
and 1003, a first transmission path 1109 between the first port
1001 and the second port 1002, and a second transmission path 1209
between the first port 1001 and the third port 1003. Each
transmission path 1109 (1209) comprises two input/output lines 1103
and 1104 (1203 and 1204), a first transmission line 1101 (1201), a
second transmission line 1102 (1202), one or more termination
switch circuits 1110-1, . . . , 1110-N (1210-1, . . . , 1210-N)
(where N is an integer greater than or equal to 1 and n in FIG. 4
is an integer between 1 and N, inclusive). The first transmission
line 1101 (1201) has one end connected to one of the input/output
lines 1103 (1203) and the other end connected to the other
input/output line 1104 (1204). The second transmission line 1102
(1202) has one end connected to one of the input/output line 1103
(1203) and the other end connected to the other input/output line
1104 (1204). Each transmission path 1109 (1209) comprises one or
more short-circuiting switches 1120-1, . . . , 1120-M (1220-1, . .
. , 1220-M) (where M is an integer greater than or equal to 1 and m
in FIG. 4 is an integer between 1 and M, inclusive). Each of the
short-circuiting switches is capable of short-circuiting between
the two transmission lines 1101 and 1102 (1201 and 1202) at points
at the same electrical length from the input/output line 1103
(1203). The set of the transmission lines 1101 and 1102 (1201 and
1202) and the input/output lines 1103 and 1104 (1203 and 1204) will
be referred to as the transmission line 1100 (1200).
[0093] The transmission line 1100 (1200) is not necessarily limited
to a straight line provided that if it satisfies the requirement
(1) to (5) described above; the transmission line 1100 (1200) may
be a curve. The electrical length of the first transmission line
1101 (1201) is equal to the electrical length of the second
transmission line 1102 (1202). The characteristic impedances for
the even mode and the odd mode of the first transmission line 1101
(1201) are constant along the length of the first transmission line
1101 (1201). The characteristic impedance for the even and odd
modes of the second transmission line 1102 (1202) are constant
along the length of the transmission line 1102 (1202). The
characteristic impedance for the even mode of the first
transmission line 1101 (1201) is equal to the characteristic
impedance for the even mode of the second transmission line 1102
(1202). The characteristic impedance for the odd mode of the first
transmission line 1101 (1201) is equal to the characteristic
impedance for the odd mode of the second transmission line 1102
(1202). The termination switch circuit 1110-n (1210-n) comprises a
switch 1111-n (1211-n) one end of which is connected to one of the
first transmission line 1101 (1201) and the second transmission
line 1102 (1202), and a termination circuit 1112-n (1212-n)
connected to the other end of the switch 1111-n (1211-n).
[0094] The first port 1001 is connected to the input/output line
1103 through lines 1013 and 1011. The first port 1001 is also
connected to the input/output line 1203 through the line 1013 and a
line 1012. The second port 1002 is connected to the input/output
line 1104 through a line 1022. The third port 1003 is connected to
the input/output line 1204 through a line 1023. The connection
point of the lines 1011, 1012 and 1013 will be referred to as the
intersection 1010 (or the intersection 1010 of two transmission
paths). The lines 1011, 1012 and 1013 depict that the first port
1001 is electrically connected to the input/output lines 1103 and
1203. In reality, the multimode frontend circuit has a length that
is negligible in design.
[0095] An operation of the multimode frontend circuit 1000
functioning as a switch (to switch between transmission lines to
propagate a signal according to time in order to support TDD) will
be described first. FIG. 5 illustrates a circuit model illustrating
the switching operation. It is assumed here that the characteristic
impedances of the parallel transmission lines are 100.OMEGA. for
the even mode and 50.OMEGA. for the odd mode for both the
transmission paths 1109 and 1209. It is also assumed here that the
electrical lengths of the parallel lines are 300.degree. at 5 GHz.
The characteristic impedance and electrical length of the
input/output line 1103 are 50.OMEGA. and 10.degree., respectively,
at 5 GHz. It is assumed that the electrical lengths in the
following description are electrical lengths at 5 GHz, unless
otherwise stated. The electrical lengths in the transmission path
1209 do not necessarily need to be the same as those in the
transmission path 1109. The termination circuit 1112-n connected to
the switch 1111-n is a ground conductor herein. It is assumed that
the transmission lines 1100 and 1200 and the switches 1111-n and
1120-m are ideal. In particular, the switches 1111-n and 1120-m are
ideal when the impedance in the off state is infinite and the
impedance in the on state is short-circuit impedance. For
simplicity, the switches 1111-1, . . . , 1111-n-1, 1111-n+1, . . .
, 1111-N, 1120-1, . . . , 1120-m-1, 1120-m+1, . . . , 1120-M,
1211-1, . . . , 1211-N, 1220-1, . . . , 1220-M which are in the off
state are omitted from FIG. 5 and only the switches 1111-n and
1120-m in the on state are depicted. The termination circuits
(here, the ground conductors as stated above) connected to the
switches in the off state are also omitted.
[0096] Requirements for causing the circuit in FIG. 5 to function
as a switch will be described below. To block signal propagation in
the transmission path 1109 (1209), the switches 1111-n and 1120-m
(1211-n and 1200-m) at the same location on the transmission line
1100 (1200) are both turned on. The location is indicated by
L.sub.S1 and the value of L.sub.S1 is determined by a method which
will be described later. For the transmission path 1109 in FIG. 5,
the switches 1111-n and 1120-m at the same location on the
transmission line 1100 are in the on state. Accordingly, a signal
with a frequency corresponding to the location of the switches
1111-n and 1120-m is blocked.
[0097] In the transmission path 1209 (1109) through which a signal
is to be propagated, on the other hand, the switches 1211-n and
1220-m (1111-n and 1120-m) at the same locations on the
transmission line 1200 (1100) are not turned on. In FIG. 5, all
switches on the transmission path 1209 are in the off state.
Accordingly, a signal input in the transmission path 1209 is output
to the third port 1003. If only a signal with a particular
frequency is to be passed through the transmission path 1209, the
switches 1211-n and 1220-m are turned on appropriately to allow the
transmission line 1200 of the transmission path 1209 to function as
filter, as will be described later. However, the switches 1211-n
and 1220-m at the same location on the transmission line 1200
should not to be turned on at the same time, as stated in the
requirements above.
[0098] How to determine the location L.sub.S1, of switches to be
turned on in a transmission path in which signal propagation is to
be blocked will be described below. FIGS. 6A, 6B, 7 and 8
illustrate impedances Z.sub.ins1 and S-parameters at L.sub.S1 of
10.degree. and 80.degree. when the transmission path 1109 is viewed
from the intersection 1010 of the transmission paths 1109 and 1209.
FIG. 6A illustrates impedance Z.sub.ins1 at frequencies between 4
and 6 GHz at L.sub.S1 of 10.degree.. FIG. 6B illustrates impedance
Z.sub.ins1 at frequencies between 4 and 6 GHz at L.sub.S1 of
80.degree.. FIG. 7 illustrates the S-parameter at L.sub.S1 of
10.degree.. FIG. 8 illustrates the S-parameter at L.sub.S1 of
80.degree.. In FIGS. 7 and 8, S11 represents the reflection
coefficient of a signal input through the first port 1001 (the line
with triangular marks), S21 represents the transmission coefficient
from the first port 1001 to the second port 1002 (the line with
square marks), and S31 represents the transmission coefficient from
the first port 1001 to the third port 1003 (the line with rhombic
marks).
[0099] The case at L.sub.S1 of 10.degree. will be described first.
At 10.degree., Z.sub.ins1 has a value close to 0 at 5 GHz. S21 is
approximately -800 dB at frequencies between 4 and 6 GHz, which
indicates that signals are successfully blocked. This is because
both of the switches 1111-n and 1120-m at location L.sub.S1 are
turned on and as a result the transmission path 1109 has become
equivalent to a short-circuit stub made up of the input/output line
1103 and a transmission line with a length of L.sub.S1 to prevent
the signals from propagating to the line on the second port side
from L.sub.S1. On the other hand, S31 at 5 GHz is approximately
-4.6 dB, which indicates that the signal has passed with a somewhat
high loss. This is because Z.sub.ins1 is small and some signals do
not propagate to the third port 1003 but is reflected to the first
port 1001. If Z.sub.ins1 were infinite, all signals input through
the first port 1001 would be transmitted to the third port 1003 as
if the transmission path 1109 from the intersection 1010 to the
second port 1002 were absent.
[0100] At L.sub.S1 of 80.degree., Z.sub.ins1 is infinite nearly
infinite at 5 GHz as apparent from FIG. 6B. At this point, S31 is
almost 0 at 5 GHz and the transmission is almost lossless. That is,
the signal has propagated to the port 1003 almost losslessly. If a
signal of 4 GHz, for example, is to be allowed to propagate with a
minimum loss, L.sub.S1 is set such that Z.sub.ins1 at 4 GHz
approaches infinite. In this way, setting L.sub.S1 such that
Z.sub.ins1 approaches infinite at a frequency near the frequency of
a signal to be propagated to the third port 1003 allows the signal
to more efficiently propagate to the third port 1003.
Variation
[0101] By making a slight change to the circuit configuration in
FIG. 4 as illustrated in FIG. 9, the operation of the switches
1111-n, 1120-m, 1211-n and 1220-m described above can be
accomplished without using short-circuiting switches 1120-1, . . .
, 1120-M (1220-1, . . . , 1220-M). FIG. 9 illustrates a
configuration of a multimode frontend circuit having termination
switch circuits attached to both of parallel lines. In the
multimode frontend circuit 1000', termination switch circuits
1130-1, . . . , 1130-M and 1230-1, . . . , 1230-M are provided in
place of the short-circuiting switches 1120-1, . . . , 1120-M and
1220-1, . . . , 1220-M.
[0102] When signal propagation in the transmission path 1109 is to
be blocked, switches 1111-n and 1131-m on the parallel lines at the
same distance from an edge are turned on. This operation will be
described with reference to a calculation model in FIG. 10. Factors
such as the lengths of lines are the same as those in FIG. 5 and
termination circuits 1112 and 1132 are ground conductors as in FIG.
5. A difference from the model in FIG. 5 is that the termination
switch circuits in the on state are at a distance L.sub.S1 on two
transmission lines 1101 and 1102 making up a transmission line 1100
of a first transmission path 1109. Because of the presence of the
on-state termination switch circuits, the impedance between the
transmission lines 1101 and 1102 will be 0 at the distance
L.sub.S1. Thus, the same impedance that can be achieved using the
short-circuiting switch 1120-m in FIG. 5 can be achieved.
Therefore, the switching operation as in the configuration in FIG.
5 can be achieved in the configuration in FIG. 10 as well. FIGS.
11A, 11B, 12 and 13 illustrate impedance Z.sub.ins1 and S-parameter
at L.sub.S1 of 10.degree. and 80.degree. in the configuration of
FIG. 10 when the transmission path 1109 is viewed from the
intersection 1010 of the transmission paths 1109 and 1209. FIG. 11A
illustrates impedance Z.sub.ins1 at frequencies between 4 and 6 GHz
at L.sub.S1 of 10.degree.. FIG. 11B illustrates impedance
Z.sub.ins1 at frequencies between 4 and 6 GHz at L.sub.S1 of
80.degree.. FIG. 12 illustrates the S-parameter at L.sub.S1 of
10.degree.. FIG. 13 illustrates the S-parameter at L.sub.S1 of
80.degree.. In FIGS. 12 and 13, S11 represents the reflection
coefficient of a signal input through the first port 1001 (the line
with triangular marks), S21 represents the transmission coefficient
from the first port 1001 to the second port 1002 (the line with
square marks), and S31 represents the transmission coefficient from
the first port 1001 to the third port 1003 (the line with rhombic
marks). It can be seen from FIGS. 11A, 11B, 12 and 13 that the same
characteristics as in FIG. 6A, 6B, 7 and 8 can be achieved. Thus,
the switching operation as in the configuration in FIG. 4 can be
accomplished in the configuration in FIG. 9. In the variation, as
in the configuration in FIG. 4, short-circuiting switches 1120-1, .
. . , 1120-M and 1220-1, . . . , 1220-M may be provided and
selectively used for an intended function.
Implementation of Filtering
[0103] A function of the multimode frontend circuit of the first
embodiment will be described with respect to the circuit
configuration in FIG. 14. In the transmission line 1200 of the
transmission path 1209 in FIG. 14, switches 1211-r, 1220-p and
1220-q are in the on state, unlike in FIGS. 5 and 10. The location
of the switch 1211-r is represented by L.sub.SF2 and the distance
between the switches 1220-p and 1220-q is represented by L.sub.FF2.
While all switches of the transmission path 1209 are turned off to
cause the transmission path 1209 to function as merely a
transmission path in FIGS. 5 and 10, the transmission path 1209 in
FIG. 14 can be caused to function as a filter by appropriately
turning on the switches 1211-r, 1220-p and 1220-q. The operation
will be described with reference to FIG. 15.
[0104] Like FIG. 5, FIG. 15 illustrates a circuit model used for
calculating characteristics of the circuit. As before, it is
assumed here that signal propagation in the transmission path 1109
is to be blocked and signal propagation in the transmission path
1209 is to be allowed. Termination circuits 1112-n and 1212-r are
ground conductors. Frequency to be passed or blocked can be
switched between 5 GHz and 4.5 GHz, for example, and the bandwidth
of the transmission path 1209 is also variable. The circuit model
for 5 GHz will be described first. The transmission path 1109 is
the same as that in FIGS. 6A, 6B, 7 and 8 and therefore description
of the transmission path 1109 will be omitted. The location of
switch 1211-r is represented by L.sub.SF2 and the location of
switch 1220-q is represented by L.sub.FF2 for the transmission path
1209. Switch 1220-p is not used in the model in FIG. 15. In this
case, the connection point (location 0) between an input/output
line 1203 and each of transmission lines 1201 and 1202 can be
considered to be the location of the switch 1220-p and therefore
the location of switch 1220-q is represented by L.sub.FF2. The
center frequency of the filter is determined by L.sub.FF2. When
L.sub.FF2 is 180.degree., the center frequency is 5 GHz. The
bandwidth is determined by L.sub.SF2. Changing the value of
L.sub.SF2 changes the bandwidth but does not change the center
frequency. That is, the center frequency and the bandwidth can be
changed independently of each other. This is one of the features of
the first embodiment. The filter is detailed in the unpublished
patent application (Japanese Patent Application No. 2010-049126)
filed by the present applicant and therefore description thereof
will be omitted.
[0105] FIG. 16 illustrates frequency characteristics when
L.sub.SF1=80.degree., L.sub.FF2=180.degree., and L.sub.SF2 is
changed between 10.degree. and 20.degree.. In FIG. 16, S11
represents the reflection coefficient of a signal input through the
first port 1001 (the line with triangular marks), S21 represents
the transmission coefficient from the first port 1001 to the second
port 1002 (the line with square marks), and S31 represents the
transmission coefficient from the first port 1001 to the third port
1003 (the line with rhombic marks). Signal propagation in the
transmission path 1109 is blocked as S21 is -800 dB. As can be
seen, the transmission path 1209 has characteristics of a filter
with a center frequency of 5 GHz, showing that the bandwidth can be
changed by changing the value of L.sub.SF2 without changing the
center frequency.
[0106] The circuit model for 4.5 Hz will be described next. In the
transmission path 1109, L.sub.SF1 in FIG. 15 is changed to
90.degree. so that Z.sub.ins1 becomes infinite at 4.5 GHz. In the
transmission path 1209, L.sub.FF2 is set to 200.degree. to change
the center frequency of the filter to 4.5 GHz. As before, the
bandwidth can be changed by L.sub.SF2 while the center frequency is
kept constant. FIG. 17 illustrates frequency characteristics when
L.sub.SF1=90.degree. and L.sub.FF2=200.degree., and L.sub.SF2 is
changed between 10.degree. and 20.degree.. It can be seen from FIG.
17 that the transmission path 1109 has characteristics that block a
signal with 4.5 GHz while the characteristics of the transmission
path 1209 shows that it is functioning as a filter with a center
frequency of 4.5 Hz. It also can be seen that the bandwidth of the
transmission path 1209 can be changed independently of the center
frequency by changing L.sub.SF2.
[0107] While the filtering characteristics of the transmission path
1209 as a one-stage filter using a single resonator has been
described, filtering characteristics of the transmission path 1209
as a filter with two or more stages can be adjusted as well by
appropriately turning on switches 1211-r, 1220-p and 1220-q. This
is detailed in the patent application given above (Japanese Patent
Application No. 2010-049126) and therefore description of such
filtering will be omitted.
Implementation of Duplex Function
[0108] A multimode frontend circuit of the first embodiment used as
a duplexer will be described below. FIG. 18 illustrates exemplary
states of switches when the multimode frontend circuit of the first
embodiment is used as a duplexer. The switches are set so that both
transmission paths 1109 and 1209 function as the filter described
above. Each transmission path has two short-circuiting switches
1120-k and 1120-m (1220-p and 1220-q) in the on state, and one
switch 1111-n (1211-r) in the on state in the segment enclosed by
the two short-circuiting switches and parallel lines. The segment
between the two short-circuiting switches 1120-k and 1120-m (1220-p
and 1220-q) functions as a resonator, which allows the transmission
path to function as a filter. Here, the distances from the starting
points of transmission lines 1101, 1102 and 1201, 1202 (the edges
connected to input/output lines 1103 and 1203, respectively) to the
on-state short-circuiting switches 1120-k and 1220-p, respectively,
closest to the starting points are L.sub.D1.sub.--.sub.1 and
L.sub.D2.sub.--.sub.1, respectively, in the transmission paths 1109
and 1209, respectively. The distances from the short-circuiting
switches 1120-k and 1220-p closest to the starting points to the
switches 1111-n and 1211-r, respectively, in the on state are
L.sub.D1.sub.--.sub.2 and L.sub.D2.sub.--.sub.2, respectively, in
the transmission paths 1109 and 1209, respectively. The lengths of
the segments of transmission lines 1100 and 1200 that function as
resonators with the two short-circuiting switches 1120-k and
1120-m, 1220-p and 1220-q in the on state are L.sub.DR1 and
L.sub.DR2, respectively, in the transmission paths 1109 and
1209.
[0109] The center frequency is determined by the length L.sub.DR1
(L.sub.DR2) of the segment, which can be changed using the
short-circuiting switches 1120-k and 1120-m (1220-p and 1220-q).
The bandwidth can be set by the switch 1111-n (1211-r)
independently of the center frequency. A remarkable feature of the
multimode frontend circuit used as a duplexer is that frequencies
to be blocked can be changed while maintaining the center
frequencies that are allowed to pass. Specifically, the starting
point of the segment that is caused to function as a resonator is
changed. For example, if the center frequency of the transmission
path 1109 is f.sub.1 and the center frequency of the transmission
path 1209 is f.sub.2, the location L.sub.D1.sub.--.sub.1 of the
short-circuiting switch 1120-k, which is the starting point of the
segment of the transmission path 1109 functioning as a resonator,
is adjusted so that Z.sub.ins1 peaks at frequency f.sub.2.
Similarly, the location L.sub.D2.sub.--.sub.1 of the
short-circuiting switch 1220-p, which is the starting point of the
segment of the transmission path 1209 functioning as a resonator,
is adjusted so that the impedance Z.sub.ins2 when the third port
1003 is viewed from the intersection 1010 of the two transmission
paths peaks at frequency f.sub.1. Such adjustments enable the
transmission path 1109 to efficiently pass a signal with the
frequency f.sub.1 and to efficiently block a signal with frequency
f.sub.2 (to direct the signal to the transmission path 1209).
Similarly, the adjustments enable the transmission path 1209 to
efficiently pass the signal with frequency f.sub.2 and to
efficiently block the signal with frequency f.sub.1 (to direct the
signal to the transmission path 1109).
[0110] The operation will be described with respect to a circuit
model in FIG. 19 and frequency characteristics in FIGS. 20 and 21.
FIG. 19 is a circuit model of the multimode frontend circuit of the
first embodiment functioning as a duplexer. Termination circuits
1112-n and 1212-n are ground conductors. FIG. 20 illustrates
frequency characteristics when L.sub.DR1=180.degree.,
L.sub.D1.sub.--.sub.1=55.degree., L.sub.D1.sub.--.sub.2=17.degree.,
L.sub.DR2=164.degree., L.sub.D2.sub.--.sub.1=52.degree., and
L.sub.D2.sub.--.sub.2=17.degree.. FIG. 21 illustrates frequency
characteristics when L.sub.DR1=200.degree.,
L.sub.D1.sub.--.sub.1=65.degree., L.sub.D1.sub.--.sub.2=17.degree.,
L.sub.DR2=183.degree., L.sub.D2.sub.--.sub.1=62.degree., and
L.sub.D2.sub.--.sub.2=17.degree.. Changing the parameters that
determine the locations of the switches in the on state enables the
multimode frontend circuit to function as a duplexer capable of
operating with variable frequency characteristics. In FIGS. 20 and
21, S11 represents the reflection coefficient of a signal input
through the first port 1001 (the line with triangular marks), S21
represents the transmission coefficient from the first port 1001 to
the second port 1002 (the line with square marks), and S31
represents the transmission coefficient from the first port 1001 to
the third port 1003 (the line with rhombic marks). It can be seen
from FIG. 20 that the passband of the transmission path 1109 is 5
GHz and the passband of the transmission path 1209 is 5.5 GHz.
Also, it can be seen from FIG. 21 that the passband of the
transmission path 1109 is 4.5 GHz and the passband of the
transmission path 1209 is approximately 4.8 GHz.
[0111] Selecting appropriately the switches 1120-1, . . . , 1120-M
and 1111-1, . . . , 1111-N (1220-1, . . . , 1220-M and 1211-1, . .
. , 1211-N) to turn on as described above enables the multimode
frontend circuit of the first embodiment to function as a switch at
times, as a switch having a filtering function at other times, and
as a duplexer at yet other times. Furthermore, the center
frequencies and bandwidths of the filter and the duplexer can be
changed independently of each other and the number of stages of the
filter and the duplexer can also be changed.
[0112] The characteristics of the multimode frontend circuit having
termination circuits 1112-n and 1212-n that are ground conductors
have been described above. However, the termination circuits 1112-n
and 1212-n are not limited to ground conductors; various circuits
illustrated in FIGS. 22A to 22Q can be connected. Furthermore, the
circuits are not limited to fixed-characteristics circuits. By
connecting variable-characteristics circuits, characteristics can
be changed more flexibly. FIGS. 22A to 22Q illustrate exemplary
combinations with a ground conductor 2001, a coil 2002, a capacitor
2003, a transmission line 2004, a variable coil 2005, a variable
capacitor 2006, and a switch 2007. However, combinations are not
limited to these.
[0113] FIG. 23 illustrates an exemplary configuration using
variable LC resonators as termination circuits 1112-n and 1212-r.
The inductances of the coils of parallel resonators used as
transmission paths 1109 and 1209 are represented by L.sub.P1 and
L.sub.P2, respectively, and the capacitances of capacitors are
presented by C.sub.P1 and C.sub.P2. By changing the characteristics
of these reactance elements, the frequency characteristics of the
transmission paths 1109 and 1209 can be changed while maintaining
the center frequencies. FIG. 24 illustrates frequency
characteristics when L.sub.DR1=180.degree.,
L.sub.D1.sub.--.sub.1=48.degree., L.sub.D1.sub.--.sub.2=35.degree.,
L.sub.DR2=164.degree., L.sub.D2.sub.--.sub.1=65.degree.,
L.sub.D2.sub.--.sub.2=25.degree., C.sub.P1=0.2 pF, L.sub.P1=0.4 nH,
C.sub.P2=4.6 pF, and L.sub.P2=0.3 nH. The passband frequencies of
the transmission paths 1109 and 1209 are 5 GHz and 5.5 GHz,
respectively, which are the same as those in FIG. 20. It can be
seen from FIG. 24 that the propagation factor of a signal
propagating through the second transmission path 1209, in
particular, significantly decreases from approximately -15 dB to
more than -40 dB at 5 GHz, showing an improvement in the degree of
signal separation.
[0114] The termination circuits 1112-n and 1212-n do not
necessarily need to be of one type; they may be designed according
to desired characteristics. While exemplary configurations using
micro-strip lines have been described above, the present embodiment
is not limited to configurations using micro-strip lines.
[0115] As has been described above, the multimode frontend circuit
of the first embodiment can provide the functions of a switch, a
switch with a filtering function, and a duplexer. Furthermore,
frequency characteristics can be changed. In particular, the center
frequencies and bandwidths of the multimode frontend circuit
functioning as a filter or duplexer can be changed independently of
each other. The number of stages of the filter and duplexer can
also be changed. Moreover, the multimode frontend circuit of the
first embodiment can be readily fabricated because the circuit can
be configured with transmission lines, switches, reactance
elements, variable reactance elements and the like.
Second Embodiment
[0116] FIG. 25 illustrates a configuration of a multimode frontend
circuit of a second embodiment. Like the multiband frontend circuit
of the first embodiment, the multimode frontend circuit of the
second embodiment may be fabricated with micro-strip lines, for
example. Like the multimode frontend circuit 1000, the multimode
frontend circuit 2000 comprises three ports, namely a first port
1001, a second port 1002 and a third port 1003, a first
transmission path 1109 between the first port 1001 and the second
port 1002 and a second transmission path 1209 between the first
port 1001 and the third port 1003. Each transmission path 1109
(1209) comprises two input/output lines 1103 and 1104 (1203 and
1204), a first transmission line 1101 (1201), a second transmission
line 1102 (1202), multiple termination switch circuits 1110-1, . .
. , 1110-N (1210-1, . . . , 1210-N) (where N is an integer greater
than or equal to 2 and n in FIG. 25 is an integer between 1 and N,
inclusive), short-circuiting switches 1120-1, . . . , 1120-M
(1220-1, . . . , 1220-M) (where M is an integer greater than or
equal to 4 and m in FIG. 25 is an integer between 1 and M,
inclusive). Specific configurations of the first transmission line
1101 (1201), the second transmission line 1102 (1202), and the
termination switch circuits 1110-n (1210-n) and the
short-circuiting switches 1120-m (1220-m) are the same as those in
the first embodiments. Requirements that the transmission line 1100
(1200) should satisfy are the same as those in the first
embodiment.
[0117] The multimode frontend circuit 2000 differs from the
multimode frontend circuit 1000 in that the multimode frontend
circuit 2000 comprises function selector switches 2141 and 2241.
The function selector switch 2141 is a switch connecting the port
1002 to one of terminals 2142 and 2143. The terminal 2142 is
connected to a port 2102 (transmission path 1109'). The terminal
2143 is connected to a port 2104 through a line 2011, an
intersection 2010, and a line 2013 (transmission path 2109). The
function selector switch 2241 is a switch that connects the port
1003 to one of terminals 2242 and 2243. The terminal 2242 is
connected to a port 2103 (transmission path 1209'). The terminal
2243 is connected to the port 2104 through a line 2012, an
intersection 2010, and a line 2013 (transmission path 2209). The
ports 1001, 1002 and 1003 relate to the input/output lines 1103,
1203, 1104 and 1204 in the same manner as in the first embodiment.
The lines 1011, 1012, 1013, 1022, 1023, 2011, 2012 and 2013 depict
electrical connections. In a real multimode frontend circuit, the
lines 1011, 1012, 1013, 1022, 1023, 2011, 2012 and 2013 may have
lengths that are negligible in design or may be designed by taking
into consideration the lengths.
[0118] With the configuration described above, when the function
selector switch 2141 connects the port 1002 to the terminal 2142
and the function selector switch 2241 connects the port 1003 to the
terminal 2242, the multimode frontend circuit 2000 becomes
practically the same in configuration as the multimode frontend
circuit 1000. Thus, the same circuit can provide the function of a
duplexer operating with variable bandwidths and center frequencies
and the function of a switch for TDD.
[0119] When the function selector switch 2141 connects the port
1002 to the terminal 2143 and the function selector switch 2241
connects the port 1003 to the terminal 2243, the multimode frontend
circuit 2000 becomes a variable dual-band filter capable of passing
signals in two frequency bands simultaneously by using the port
1001 as an input port and the port 2104 as an output port.
Implementation of Variable Dual-Band Filter Function
[0120] The principle and an example of operation of the multiband
frontend circuit functioning as a variable dual-band filter will be
described below. To cause the multiband frontend circuit to
function as a variable dual-band filter, it is desirable that the
transmission coefficient of the filter in a passband be as large as
possible (insertion loss be as small as possible). Let F1 denote a
passband frequency of the transmission paths 1109 and 2109 and F2
denote a passband frequency of the transmission paths 1209 and
2209. A signal with frequency F1 needs to be transmitted to the
transmission paths 1109 and 2109 as losslessly as possible and a
signal with frequency F2 needs to be transmitted to the
transmission paths 1209 and 2209 as losslessly as possible. To
achieve this, the impedance Z.sub.11 when the transmission paths
1109 and 2109 are viewed from the intersection 1010 and the
impedance Z.sub.41 when the transmission paths 2109 and 1109 are
viewed from the intersection 2010 need to be infinite or nearly
infinite at frequency F2, and the impedance Z.sub.12 when the
transmission paths 1209 and 2209 are viewed from the intersection
1010 and the impedance Z.sub.42 when the transmission paths 2209
and 1209 are viewed from the intersection 2010 need to be infinite
or nearly infinite at frequency F1. The following example shows
that the transmission coefficient in the passband can be increased
(that the transmission coefficient can be reduced to nearly 0 dB)
by controlling the multimode frontend circuit 2000 so that the
conditions given above are satisfied.
[0121] FIG. 26 illustrates a configuration of the multimode
frontend circuit 2000 functioning as a variable dual-band filter.
First, the function selector switch 2141 connects the port 1002 to
the terminal 2143 and the function selector switch 2241 connects
the port 1003 to the terminal 2243. In the first transmission path
1109, four short-circuiting switches 1120-m.sub.1, . . . ,
1120-m.sub.4 (where m.sub.1, . . . , m.sub.4 are integers between 1
and M, inclusive, and m.sub.1<m.sub.2<m.sub.3<m.sub.4) are
turned on and the other short-circuiting switches are turned off.
Also in the first transmission path 1109, two termination switch
circuits 1110-n.sub.1 and 1110-n.sub.2 (where n.sub.1 and n.sub.2
are integers between 1 and N, inclusive, and n.sub.1<n.sub.2)
are turned on and the other termination switch circuits are turned
off. In the second transmission path 1209, four short-circuiting
switches 1220-k.sub.1, 1220-k.sub.4 (where k.sub.1, . . . , k.sub.4
are integer between 1 and M, inclusive, and
k.sub.1<k.sub.2<k.sub.3<k.sub.4) are turned on and the
other short-circuiting switches are turned off. Also in the second
transmission path 1209, two termination switch circuits
1210-h.sub.1 and 1210-h.sub.2 (where h.sub.1 and h.sub.2 are
integers between 1 and N, inclusive, and h.sub.1<h.sub.2) are
turned on and the other termination switch circuits are turned off.
Distributed constant lines 2004 connected to a ground conductor
2001 are used as the termination circuits 1112-1, . . . , 1112-N
and 1212-1, . . . , 1212-N of the termination switch circuits
1110-1, . . . , 1110-N and 1210-1, . . . , 1210-N.
[0122] The length of the first and second transmission line 1101
and 1102 of the first transmission path 1109 is
L.sub.A.sub.--.sub.1, the length of the input/output line 1103 is
L.sub.TLin.sub.--.sub.1, the length of the input/output line 1104
is L.sub.TLout.sub.--.sub.1, the distance between the input/output
line 1103 and the short-circuiting switch 1120-m.sub.1 is
L.sub.in.sub.--.sub.1, the distance between the short-circuiting
switch 1120-m, and the short-circuiting switch 1120-m.sub.2 is
L.sub.1.sub.--.sub.1, the distance between the short-circuiting
switch 1120-m.sub.2 and the short-circuiting switch 1120-m.sub.3 is
L.sub.1.sub.--.sub.1/2, the distance between the short-circuiting
switch 1120-m.sub.3 and the short-circuiting switch 1120-m.sub.4 is
L.sub.1.sub.--.sub.1, the distance between the short-circuiting
switch 1120-m.sub.1 and the termination switch circuit 1110-n.sub.1
is L.sub.2.sub.--.sub.1, the distance between the short-circuiting
switch 1120-m.sub.3 and the termination switch circuit 1110-n.sub.2
is L.sub.3.sub.--.sub.1, the length of the transmission line 2004
of the termination circuit 1112-n.sub.1 is L.sub.4.sub.--.sub.1,
and the length of the transmission line 2004 of the termination
circuit 1112-n.sub.2 is L.sub.5.sub.--.sub.1. The length of the
first and second transmission lines 1201 and 1202 of the second
transmission path 1209 is L.sub.A.sub.--.sub.2, the length of the
input/output line 1203 is L.sub.TLin.sub.--.sub.2, the length of
the input/output line 1204 is L.sub.TLout.sub.--.sub.2, the
distance between the input/output line 1203 and the
short-circuiting switch 1220-k.sub.1 is L.sub.in.sub.--.sub.2, the
distance between the short-circuiting switch 1220-k.sub.1 and the
short-circuiting switch 1220-k.sub.2 is L.sub.1.sub.--.sub.2, the
distance between the short-circuiting switch 1220-k.sub.2 and the
short-circuiting switch 1220-k.sub.3 is L.sub.1.sub.--.sub.2/2, the
distance between the short-circuiting switch 1220-k.sub.3 and the
short-circuiting switch 1220-k.sub.4 is L.sub.1.sub.--.sub.2, the
distance between the short-circuiting switch 1220-k.sub.1 and the
termination switch circuit 1210-h.sub.1 is L.sub.2.sub.--.sub.2,
the distance between the short-circuiting switch 1220-k.sub.3 and
the termination switch circuit 1210-h.sub.2 is
L.sub.3.sub.--.sub.2, the length of the transmission line 2004 of
the termination circuit 1212-h, is L.sub.4.sub.--.sub.2 and the
length of the transmission line 2004 of the termination circuit
1212-h.sub.2 is L.sub.5.sub.--.sub.2.
[0123] FIG. 27 illustrates the transmission coefficient from the
port 1001 to the port 2104 when the electrical lengths at 5 GHz are
set as follows: L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=57.degree., L1.sub.--.sub.1=180.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=155.degree., L.sub.5.sub.--.sub.1=155.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=73.degree., L.sub.1.sub.--.sub.2=160.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=155.degree. and
L.sub.5.sub.--.sub.2=11.degree.. The horizontal axis of the graph
in FIG. 27 represents frequency and the vertical axis represents
transmission coefficient (dB). Under the conditions given above,
there are passbands of 5 GHz and 5.62 GHz and the transmission
coefficient in the two passbands is almost 0 dB. Since the
electrical length L.sub.1.sub.--.sub.1 is 180.degree. at 5 Hz, the
passband of the transmission paths 1109 and 2109 is 5 GHz. The
electrical length L.sub.1.sub.--.sub.2 at 5 Hz is 160.degree.,
which is 180.degree. at 5.62 GHz. Accordingly, the passband of the
transmission paths 1209 and 2209 is 5.62 GHz.
[0124] FIG. 28A is a Smith chart illustrating impedances Z.sub.11
and Z.sub.41 at 5.62 GHz in FIG. 27. FIG. 28B is a Smith chart
illustrating impedances Z.sub.12 and Z.sub.42 at 5 GHz in FIG. 27.
As can be seen, the impedances Z.sub.11 and Z.sub.41 at 5.62 GHz
are infinite or nearly infinite. Accordingly, a signal with 5.62
GHz does not propagate to the transmission paths 1109 and 2109 but
propagates through the transmission paths 1209 and 2209, then is
output through the port 2104. The impedances Z.sub.12 and Z.sub.42
at 5 Hz are infinite or nearly infinite. Accordingly, a signal with
5 GHz does not propagate to the transmission paths 1209 and 2209
but propagates through the transmission paths 1109 and 2109, then
is output through the port 2104.
[0125] FIG. 29 illustrates the transmission coefficient from the
port 1001 to the port 2104 when the electrical lengths at 5 GHz are
set as follows: L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=57.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=155.degree., L.sub.5.sub.--.sub.1=155.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=73.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=155.degree. and
L.sub.5.sub.--.sub.2=11.degree.. The conditions in FIG. 29 differ
from the conditions in FIG. 27 only in the lengths
L.sub.1.sub.--.sub.1, and L.sub.1.sub.--.sub.2. The horizontal axis
of the graph in FIG. 29 represents frequency and the vertical axis
represents transmission coefficient (dB). The electrical length
L.sub.1.sub.--.sub.1 is 150.degree. at 5 GHz and 180.degree. at 6
GHz. Accordingly the passband of the transmission paths 1109 and
2109 would be 6 GHz. The electrical length L.sub.1.sub.--.sub.2 is
145.degree. at 5 GHz and 180.degree. at 6.18 GHz. Accordingly, the
passband of the transmission paths 1209 and 2209 would be 6.18 GHz.
As can be seen from FIG. 29, however, the transmission coefficients
at 6 GHz and 6.18 GHz, which would be the passbands, are small.
[0126] FIG. 30A is a Smith chart illustrating impedances Z.sub.11
and Z.sub.41 at 6.18 GHz in FIG. 29. FIG. 30B is a Smith chart
illustrating impedances Z.sub.12 and Z.sub.42 at 6 GHz in FIG. 29.
The impedances Z.sub.11 and Z.sub.41 at 6.18 GHz are far from
infinite (the impedances are small). Also, the impedances Z.sub.12
and Z.sub.42 at 6 GHz are far from infinite (the impedances are
small). This means that the multimode frontend circuit cannot be
caused to function as a variable dual-band filter with a large
transmission coefficient by adjusting only L.sub.1.sub.--.sub.1 and
L.sub.1.sub.--.sub.2, which are resonator lengths.
[0127] Therefore, in addition to the resonator lengths
(L.sub.1.sub.--.sub.1 and L.sub.1.sub.--.sub.2), other lengths are
adjusted so that the impedances Z.sub.11 and Z.sub.41 approach
infinite at 6.18 GHz and the impedances Z.sub.12 and Z.sub.42
approach infinite at 6 GHz. FIG. 31 illustrates the transmission
coefficient from the port 1001 to the port 2104 when the electrical
lengths at 5 GHz are set as follows:
L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=0.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=180.degree. and
L.sub.5.sub.--.sub.2=139.degree.. The horizontal axis of the graph
in FIG. 31 represents frequency and the vertical axis represents
transmission coefficient (dB). The transmission coefficient is
almost 0 dB in 6-GHz and 6.18-GHz passbands. The conditions in FIG.
31 are different from the conditions in FIG. 29 in lengths
L.sub.in.sub.--.sub.1, L.sub.4.sub.--.sub.1, L.sub.5.sub.--.sub.1,
L.sub.in.sub.--.sub.2, L.sub.4.sub.--.sub.2 and
L.sub.5.sub.--.sub.2. Especially, the lengths L.sub.in.sub.--.sub.1
and L.sub.in.sub.--.sub.2 are parameters that determine the
distance from the input/output line to the first resonator and act
as variable phase shifters. This solution uses the characteristic
of a variable filter that the parallel lines can be caused to
function both as a resonator and merely as a transmission line.
[0128] FIG. 32A is a Smith chart illustrating impedances Z.sub.11
and Z.sub.41 at 6.18 GHz in FIG. 31. FIG. 32B is a Smith chart
illustrating impedances Z.sub.12 and Z.sub.42 at 6.18 GHz in FIG.
31. As shown, the impedances Z.sub.11 and Z.sub.41 are nearly
infinite at 6.18 GHz. Accordingly, a signal with a frequency of
6.18 GHz does not propagate to the transmission paths 1109 and 2109
but propagates through the transmission paths 1209 and 2209, then
is output through the port 2104. Also, the impedances Z.sub.12 and
Z.sub.42 are nearly infinite at 6 GHz. Accordingly, a signal with a
frequency of 6 GHz does not propagate to the transmission paths
1209 and 2209 but propagates through the transmission paths 1109
and 2109, then is output through the port 2104. Thus, under the
conditions in FIG. 31, the transmission coefficient is almost 0 dB
in the 6-GHz and 6.18-GHz passbands.
[0129] An example of changing the bandwidth of a passband will be
described below. FIG. 33 illustrates the transmission coefficient
from the port 1001 to the port 2104 when the electrical lengths at
5 GHz are set as follows: L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=8.degree., L.sub.3.sub.--.sub.1=8.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.220.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=0.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=10.degree., L.sub.3.sub.--.sub.2=10.degree.,
L.sub.4.sub.--.sub.2=180.degree. and
L.sub.5.sub.--.sub.2=139.degree. . The horizontal axis of the graph
in FIG. 33 represents frequency and the vertical axis represents
transmission coefficient (dB). The dashed curve represents the
transmission coefficient under the conditions given above and the
solid curve represents the transmission coefficient under the
conditions in FIG. 31. The conditions in FIG. 33 differ from the
conditions in FIG. 31 only in the lengths L.sub.2.sub.--.sub.1 and
L.sub.3.sub.--.sub.1. It can be seen that the change of the lengths
on the transmission paths 1109, 2109 side significantly changes the
bandwidth in the 6-GHz band but does not significantly change the
bandwidth in the 6.18 GHz. It can also be seen that the center
frequency of the 6-GHz band is kept constant. This solution uses
the characteristic of a variable filter that the bandwidth can be
changed while keeping the center frequency constant.
[0130] FIG. 34 illustrates the transmission coefficient from the
port 1001 to the port 2104 when the electrical lengths at 5 GHz are
set as follows: L.sub.A.sub.--.sub.1=720.degree.,
L.sub.TLin.sub.--.sub.1=20.degree.,
L.sub.TLout.sub.--.sub.1=20.degree.,
L.sub.in.sub.--.sub.1=47.degree., L.sub.1.sub.--.sub.1=150.degree.,
L.sub.2.sub.--.sub.1=10.degree., L.sub.3.sub.--.sub.1=10.degree.,
L.sub.4.sub.--.sub.1=132.degree., L.sub.5.sub.--.sub.1=30.degree.,
L.sub.A.sub.--.sub.2=720.degree.,
L.sub.TLin.sub.--.sub.2=20.degree.,
L.sub.TLout.sub.--.sub.2=20.degree.,
L.sub.in.sub.--.sub.2=0.degree., L.sub.1.sub.--.sub.2=145.degree.,
L.sub.2.sub.--.sub.2=8.degree., L.sub.3.sub.--.sub.2=8.degree.,
L.sub.4.sub.--.sub.2=180.degree. and
L.sub.5.sub.--.sub.2=139.degree.. The horizontal axis of the graph
in FIG. 34 represents frequency and the vertical axis represents
transmission coefficient (dB). The dashed curve represents the
transmission coefficient under the conditions given above and the
solid curve represents the transmission coefficient under the
conditions in FIG. 31. The conditions in FIG. 34 differ from the
conditions in FIG. 31 only in the lengths L.sub.2.sub.--.sub.2 and
L.sub.3.sub.--.sub.2. It can be seen that the change of the lengths
on the transmission paths 1209, 2209 side significantly changes the
bandwidth in the 6.18-GHz band but does not significantly change
the bandwidth in the 6-GHz band. It can also be seen that the
center frequency of the 6.18-GHz band is kept constant. This
solution uses the characteristic of a variable filter that the
bandwidth can be changed while keeping the center frequency
constant.
[0131] The termination circuits 1112-1, . . . , 1112-N and 1212-1,
. . . , 1212-N of the termination switch circuits 1110-1, . . . ,
1110-N and 1210-1, . . . , 1210-N in FIG. 26 use the transmission
line 2004 connected to the ground conductor 2001. However, other
circuits, including but not limited to, the circuits illustrated in
FIGS. 221, 22J, 22K, 22N and 22Q can be used instead.
[0132] As described above, the multimode frontend circuit of the
second embodiment can be configured to have the configuration
equivalent to that of the multimode frontend circuit of the first
embodiment by switching the function selector switches.
Accordingly, the multimode frontend circuit of the second
embodiment offers the same effects as those of the multimode
frontend circuit of the first embodiment. Furthermore, the
multimode frontend circuit of the second embodiment can be caused
to function as a variable dual-band filter as well by appropriately
setting the function selector switches. When the multimode frontend
circuit of the second embodiment is caused to function as a
variable dual-band filter, the center frequency and bandwidth of
each passband can be changed individually.
* * * * *